November 2017 – A 3D Printed Critter

November 2017 – A 3D Printed Critter

By Jason Morgan

Everyone has heard of 3D printing: the miracle process that can make any shape. It’s gradually changing the way that manufacturing works (especially rapid prototyping). The question that the world really needs to know though: Can I make a 16mm scale diesel with it? As you can see the answer is yes; but how easy is it?

The boxcab’s unusual design came from our love of a different scale: American 0n30. This is the American 0-gauge scale, but on 16.5mm gauge track. Thanks to the huge variety of different equipment used on the American narrow gauge, 0n30 features all sorts of models: Forneys and 2-8-0s, down to tiny 0-4-0 Porters and Shays. A company called Boulder Valley Models produced a kit for a small 0-4-0 Boxcab critter. This particular diesel looked very industrial and featured a large American headlight, lots of interesting panels and a wealth of rivet detail: a good excuse to make a 3D printed diesel with lots of depth…

The exciting, futuristic bit

The Boxcab critter was thought up as a “quick” project that I could do as part of my first year Apprenticeship projects. The college I was attending was equipped with 2 Cel Robox 3D printers. These use the “extruded deposit” method for additive manufacturing, the most common for small scale plastic printers. Simply put, the print head melts a plastic filament and draws out the shape with this melted filament. The deposit then solidifies and hardens. The process builds up the shape a layer at a time until it is complete.

Before you can print a model you need to draw it. Using the AutoCAD package from work, I created a 3D model of each side (and floor), with locating tabs and recesses. I could have modelled the unit as one whole piece; however, the 3D printer I was using could not travel far enough in the Z (vertical) axis to do it.

Once I finished the design I converted it to an STL. file. This reformats the model into a format that the printer could understand. The STL. format allows easy conversion to a CAM program by the printing software. Once this was done, the model was loaded onto the Robox program and the print was set-up. The software (luckily) told me the estimated time of each print.

Unfortunately, time is the weakness of 3D printing; it is a slow process. A very slow process! At maximum resolution, where detail is most crisp, each side would have taken an agonising 16 hours! As I was not allowed to use it overnight, I had to reduce the time to 8 hours. This unfortunately meant I had to decrease the resolution per print, so I lost dimensional and detailing quality. This also meant that the tabs and recesses required a lot more cleaning than I initially wanted.

Finishing off: conventional building methods

Once I had finished printing and cleaning; I assembled the body and painted it. To hide the low resolution; I decided to heavily weather the body to give it a more “industrial” finish. Wire mesh was added to the engine compartment windows and the other windows were glazed. A rolled aluminium roof was made, with roof detail turned up from brass and soldered together.

The chassis side plates were machined from steel plate, with the stretchers from brass. Connecting rods, cranks, wheels, gears and motor were provided by Essel Engineering. The motor was connected to a Brian Jones speed controller and a potentiometer providing the speed adjustment.

So… my verdict?

The critter is a good back-up runner and ideal for use on our exhibition layout for when a steam engine is being brewed up. It is capable of pulling a handful of wagons, providing a good “industrial” consist for the diesel.

The original question was whether or not 3D printing can be used to easily make a diesel? I’d comfortably say yes! Download some CAD software and give it a go!